FIG. 9 shows a representative configuration diagram of a lighting bulb. FIG. 9 is a configuration diagram of an LED bulb which realizes a large light distribution. As shown in FIG. 9, a base 2 mounting a semiconductor light-emitting element 21 is fixed to an aluminum plate 1. In addition, a first reflection plate 31 and a second reflection plate 32 are fixed to the aluminum plate 1. A heat sink 4 is fixed around the aluminum plate 1, and a bracket 5 is fixed to a lower part of the heat sink 4. A power supply circuit (not shown) is provided in a void space surrounded by the aluminum plate 1, the heat sink 4, and the bracket 5, and a globe 6 for protecting the base 2 is fixed to an upper surface of the aluminum plate 1.
Light emitted from the semiconductor light-emitting element 21 is divided into a light 71 which passes through a window part 311 of the first reflection plate 31 and goes straight, a light 72 which passes through the window part 311 of the first reflection plate 31, is reflected by the second reflection plate 32, and changes its direction to a lateral direction, and a light 73 which is reflected by the first reflection plate 31, and changes its direction to a lower direction. In order to increase a light distribution angle of this bulb, it is preferable that the light 73 which is reflected by the first reflection plate 31 and passes through the globe 6 be diffused by the globe 6. Therefore, as a material of the globe, a synthetic resin material containing a diffusion material is used in general.
In order to make the light distribution uniform, a shape of the globe 6 preferably has a spherical or ellipsoidal body. In order to utilize more backward light, an outer diameter of the globe 6 is preferably larger than an outer diameter of the heat sink 4. That is, the shape of the globe 6 preferably has a pouched shape. Therefore, according to a conventional method for producing the globe 6 mainly used, a cylindrical intermediate product having a bottom is previously produced by an injection molding method, and the intermediate product is expanded by compressed air in a blow molding die, whereby it can be molded into a desired globe shape.
A process for producing the globe by the conventional blow molding method will be described with reference to FIGS. 10(a) to 10(d). FIG. 10(a) is a view showing a state in which an intermediate product 8 (parison) molded by the injection molding method and inserted in a rod-shaped heating apparatus to be previously softened is set in a blow molding die 10 and the blow molding die 10 is closed. Then, the intermediate product 8 is expanded with compressed air supplied from a supply port 11. FIG. 10(b) is a view showing a state in which the intermediate product 8 is expanded with the compressed air and molded into a desired globe shape.
FIG. 10(c) is a view showing a shape of the globe 6 molded by the above-described method. In the blow molding, it is necessary to strongly press the intermediate product 8 against a holder part 9 which supplies the compressed air to the intermediate product 8 so as to prevent the air from leaking to the holder part 9. Therefore, a presser margin 82 having a projection is provided in the intermediate product 8, and the intermediate product 8 is strongly fixed to the holder part 9 by a presser jig through the presser margin 82. The presser margin 82 is cut at a cut surface 12 after molded, whereby the globe shape is formed as shown in FIG. 10(d).
According to PTL 1, the globe 6 is produced by a method in which a synthetic resin sheet is fixed to a jig by vacuum suction, expanded in a molding die with compressed air, and formed into a desired globe shape, and then an unnecessary part is cut.
The method of the PTL 1 is described with reference to FIGS. 11(a) to 11(f). As shown in FIG. 11(a), a molding apparatus is prepared such that a clamp 403 is arranged on a split die 402 for blow molding, and a rod-shaped plug 404 is arranged above the clamp 403. The split mold 402 is split to right and left and stands by. A synthetic resin sheet 401 is sandwiched between the clamp 403. The synthetic resin sheet 401 has been previously heated and softened, and horizontally fixed as it is sandwiched by the clamp 403.
As shown in FIG. 11(b), when the plug 404 is lowered, the heated and softened synthetic resin sheet 401 is pressed vertically with a spherical-shaped end of the plug 404, and extended into the split mold 402 below an opening 405 of the clamp 403.
The plug 404 has several venting holes 406 in its periphery wall. The venting holes 406 are connected to a vacuum apparatus and a compressed air generation apparatus (not shown) through a passage 407 in an attachment part. As shown in FIG. 11(c), when the vacuum apparatus is activated, and the softened synthetic resin sheet 401 is immediately drawn by vacuum through the venting holes 406 of the plug 404, the synthetic resin sheet 401 becomes a synthetic resin sheet 410 adhering to the plug 404.
Then, as shown in FIG. 11(d), the split die 402 is closed. Then, as shown in FIG. 11(e), when the compressed air generation apparatus is activated and compressed air is ejected from the venting holes 406, the synthetic resin sheet 410 adhered to the plug 404 is adhered to a die surface 408 of the split die 402.
Then, as shown in FIG. 11(f), the split die 402 is opened, the clamp 403 is opened, and a molded product 409 is taken out.
The unnecessary part of the molded product 409 which has been taken out is cut in a next step, whereby the globe 6 is formed.